Repulsion between calcite crystals and grain detachment during water-rock interaction

Abstract

Weathering in carbonate rocks is often thought to be governed by chemical dissolution. However, recent studies have shown that mechanical detachment of tiny grains contributes significantly to the overall surface retreat. Whether this detachment is caused by shear forces acting at the surface, or repulsive forces acting between grains, was not known. In this study, we used atomic force microscopy to examine the mechanism of grain detachment and we demonstrate that it occurs even in the absence of shearing fluid flow. This suggests that the removal of grains from rock surfaces can be caused by repulsive forces between calcite grains. Although these repulsive forces are expected to be sensitive to the ionic strength of the solution, we did not find enough evidence to demonstrate a correlation between salinity and the frequency of grain detachment. Importantly, our findings suggest that grain detachment occurs during water-rock interaction under low flow conditions over a range of salinities, with potential impacts on geological carbon sequestration and enhanced oil recovery in carbonate formations.